With increased Internet traffic of recent years, there is an increasing demand for high-speed packet transmission techniques in mobile communication, and an OFDM (Orthogonal Frequency Division Multiplex) scheme is studied as one of the transmission schemes that realize high-speed packet transmission. The OFDM scheme can reduce degradation of performances due to multipath interference by transmitting data streams in parallel using a plurality of subcarriers and providing CP's (Cyclic Prefixes), and is robust against frequency selective fading by adopting error correcting coding.
It is studied to use resource allocation schemes such as an LRB (Localized Resource Block) and DRB (Distributed Resource Block) resource allocation scheme when this OFDM is applied in downlink and data for a plurality of mobile stations is frequency-multiplexed on a plurality of subcarriers (for example, see Non-Patent Document 1).
With the LRB scheme, the base station performs the frequency scheduling to which subcarriers are allocated adaptively, based on the received quality of each frequency band in the mobile stations, so that it is possible to maximize the multiuser diversity effect and perform communication efficiently. Frequency scheduling is normally performed per resource block (RB) which puts together several neighboring subcarriers located approximately coherent frequency band adjacent to each other, into a block. Therefore, little frequency diversity effect is provided.
By contrast with this, the DRB scheme allocates transmission data for the mobile stations in a distributed manner over the entire band of subcarriers, so that it is possible to provide a high frequency diversity effect. Further, the DRB scheme allocates transmission data regardless of the received quality of each mobile station and therefore cannot provide the frequency scheduling effect and the multiuser diversity effect as in the LRB scheme.
Meanwhile, a technique called TTI (Transmission Time Interval) concatenation is studied recently. TTI concatenation is a technique of connecting a plurality of subframes and treating them as one TTI. Therefore, for example, control information common to the plurality of subframes is added to the head of the TTI after connection. In this way, with TTI concatenation, only one control information is reported for a plurality of subframes, so that it is possible to reduce an overhead required for control information of the subsequent subframe. In Non-Patent Document 2, this TTI concatenation is referred to as “long TTI” or “adaptive TTI.”
Non-Patent Document 1: “Physical Channel Structure and Procedure for EUTRA Downlink,” 3GPP RAN WG1 #42 meeting (2005.8) R1-050884
Non-Patent Document 2: “Physical Channel Structure for Evolved UTRA,” 3GPP RAN WG1 #41 meeting (2005.3) R1-050464